1. Field of the Invention
The invention relates to resin intermediates and their preparation. The invention also relates to hydroxyl-functional, water-dispersible polymers formed from the intermediates and compositions containing the water-dispersible polymers. A preferred composition of the invention is a zero volatile organic content (VOC), ambient-cure enamel composition which contains a hydroxyl-functional, water-dispersible polyester.
2. Background of the Invention
Industrial coatings, such as paints, have commonly employed solvent systems as a means to disperse polyester and polyacrylic coating resins. Due to the presence of volatile organic solvents, these industrial coatings are often detrimental to the environment. In an effort to limit the amounts of these volatile solvents and prevent environmental damage, recent regulations have encouraged the development of water-dispersible polyester coating compositions.
Water-dispersible polyesters have numerous applications, such as in the preparation of enamel and other coating compositions. Typically, a polyester is rendered water-dispersible by neutralizing residual carboxylic acid groups on the polyester with amines. Generally, water-dispersible polyesters have an acid number of 50 or greater so that they readily disperse in water. Unfortunately, such water-dispersible polyesters have not proven entirely satisfactory. For example, coatings prepared with these resins often exhibit poor water resistance due to the presence of carboxyl groups and residual amine. Also, the presence of the residual amines may cause odor and yellowing problems in ambient-cure systems.
To ameliorate the problems with amine neutralized polyesters, polyester resins formed from 5-(sodiosulfo)-isophthalic acid (5-SSIPA) have been widely investigated for the production of water-resistant coatings. Typically, these 5-SSIPA resins are hydroxyl-functionalized and possess very low acid numbers, generally less than 5. As a result of their low acid number, 5-SSIPA resins do not require amines to make them water-dispersible. Due to the absence of the residual amine groups, coatings prepared from 5-SSIPA resins are generally odor-free and demonstrate improved water resistance. In addition, 5-SSIPA resins and coatings made from them generally do not require the presence of an organic solvent, thereby making them less detrimental to the environment.
Unfortunately, previous attempts at forming polyesters by directly copolymerizing 5-SSIPA monomers with glycols and dicarboxylic acids have proven problematic. For example, when using the sodium salt of a 5-SSIPA monomer, the presence of the salt can lead to hazy resins due to the poor solubility of these salts in the polymerization reaction mixture. This problem becomes particularly apparent when attempting to incorporate a higher ratio of 5-SSIPA into the resin. Another problem with using 5-SSIPA is that when it is copolymerized with a diol and a dicarboxylic acid in a resin synthesis reaction, the 5-SSIPA molecules often end up at ends of the polyester chains, causing the final resin to have a high acid number. Resins having such a relatively high acid number may lead to stability problems.
Attempts have been made to resolve the problems relating to the formation of polyesters containing 5-SSIPA monomers. For example, U.S. Pat. No. 5,218,042 relates to polyesters containing 5-SSIPA monomers that have been formed from sulfomonomers which have their carboxylic acid groups capped with a glycol prior to polymerization of the polyester. Typically, when capping the carboxylic acid groups of the sulfomonomers, a large excess of glycol is employed. When using large excesses of glycol, the glycol has a tendency to enter the gaseous phase. The removal of a gaseous glycol component may cause problems for a polyesterification apparatus.
In addition to water-dispersible polyesters, sulfomonomers have been used to form water-dissipatible alkyl resins for cross-linked coatings. For example, U.S. Pat. No. 5,378,757 discloses reacting at least one monoglyceride, a polycarboxylic acid, and a polyol sulfomonomer adduct containing at least one sulfonate group.
Previous attempts at forming resin intermediates from glycol components and difunctional sulfomonomers have not been fully optimized for full scale industrial production. One problem occurring in previous resin intermediates is that typically large excess amounts of the glycol component are reacted with the difunctional sulfomonomer in order to avoid the presence of unreacted difunctional sulfomonomer. Yet, resin intermediates which contain large amounts of excess glycol component restrict the types of polyesters which can be formed from the resin intermediates.
There exists a need in the art for a versatile resin difunctional sulfomonomer resin intermediate that could be produced on an industrial scale. It is desired that such resin intermediates are capable of being isolated and stored for later usage in various waterborne syntheses, such as the formation of water-dispersible polyesters.
The invention relates to polyester difunctional sulfomonomer intermediate resins. More particularly, the invention provides intermediate resins which are substantially free of unreacted, difunctional sulfomonomer particles and which may be isolated as solids and formed into loose solid forms, such as powders. These powders may be conveniently stored without caking. When desired, the intermediate resins can be easily reacted with a glycol component and a dicarboxylic acid component to form polyester resins having high levels of difunctional sulfomonomers.
More specifically, the invention relates to resin intermediates comprising the reaction products of a glycol component and a difunctional sulfomonomer, wherein the resin intermediate formed is substantially free of unreacted difunctional sulfomonomer particles. Preferably the resin intermediate is in the form of a solid, such as a powder and is storage stable, i.e., does not noticeably degrade, at room temperature.
Another embodiment of the invention relates to processes for forming the resin intermediates. One such process for forming a resin intermediate involves forming a slurry of a glycol component, a difunctional sulfomonomer and water. While in the form of a slurry, the glycol component and the difunctional sulfomonomer are reacted to form a resin intermediate, such that the resin intermediate is substantially free of unreacted difunctional sulfomonomer particles.
The invention also relates to water-dispersible polymers, such as polyesters and alkyds, which are made from the intermediate resins. Preferably, the water-dispersible polymers are hydroxyl-functional, water-dispersible polyesters. These water-dispersible polyesters are formed from about 8 to about 16 mole percent of a resin intermediate, about 35 to about 55 mole percent of at least one polyol component, and about 30 to about 50 mole percent of a diacid component. These water-dispersible polyesters can be used in a variety of applications, such as VOC free aqueous dispersions.